1. Field of the Invention
The present invention relates to a gas-discharge lamp, in particular an ultraviolet (UV) lamp.
2. Related Art
There are generally two kinds of UV lamps: cold-cathode lamps and hot-cathode lamps. Hot-cathode UV lamps have the disadvantages of being bulky, having short life spans, being unstable, having low radiant intensity, and decreasing in radiant intensity over time because the coating of the filament oxidizes so quickly, evaporates and peels off. Cold-cathode UV lamps have a higher resistance to damage from shaking and longer life spans than hot-cathode UV lamps. Cold-cathode lamps have been used in many types of liquid crystal displays (LCDs), scanners, and other such technologies because of its symmetrical, high intensity radiance and the fact that they can be made into very fine objects of various shapes.
Cold-cathode lamps are very bright and highly efficient. They also consume a lower amount of energy and have a long life span. Furthermore, cold-cathode lamps have good resistance to damage from shaking. Such lamps can restart easily and start even in lower temperatures. Compared to hot-cathode lamps, cold-cathode lamps emit less heat, are smaller in diameter, and can be used as the lighting source for LCD screens.
Conventional cold-cathode UV lamps, as shown in FIG. 1, are comprised of a glass shell 4, an electrode 5 that is set on the end of the lamp, and a fluorescent coating 6 on the inner surface of the glass shell. The emitting ability of prior art lamps is not very good because of the dispersion and scattering of electrons which do not allow for greater brightness. The brightness of the lamp depends on the amount of electric current applied to it; in this way, an increase in temperature affects the life of the lamp. The typical rated life spans of cold-cathode lamps are about 20,000 hrs, but the actual life span is much shorter due to variables such as number of times lamps are switched on and off as well as operating temperature. In addition, since the thermal requirement of the electrode is significant, (i.e. the electrode needs to be heated up enough to vaporize the mercury inside the lamp) the lamp requires some time to start after an electric current is applied.